The present invention relates to a method and apparatus for measuring the mass, or weight, of individual objects. The invention is particularly useful for measuring the mass or weight of diamonds or other precious or semi-precious stones, especially the smaller diamonds, e.g. of up to about 1 carat (100 points), and the invention is therefore described below with respect to this application.
Since the value of a diamond or other precious stone depends to a high degree on its carat weight, it is important to measure the weight of the stones as accurately as possible. One traditional way of doing this is by the use of scales or pan balances. However, such traditional methods are time-consuming, and are therefore not practical with very small stones, such as stones of up to about 50 points (00.50 carats). Such small stones are therefore generally sold in the form of parcels, e.g. a parcel of 1000 stones, of 35 points average. However, since the value of stones increases inordinately with its size, it will be appreciated that sorting even such parcels of stones into groups more precisely representing their actual weight, would greatly add to the overall value of the respective parcel of stones.
Sieves or hole gauges are also used for sorting large quantities of small polished stones, e.g. less than 100 points. Such sieves or hole gauges generally include a steel plate with a grid of accurate holes according to the size of the stones to be sorted. While such sieves and hole gauges permit sorting large numbers of small stones, each group produced by their use includes a relatively large range of stone weights.
At the present time, therefore, there is a critical need for measuring the weight of small objects in general, and small diamonds or other precious stones in particular, at a relatively high rate and with a relatively high degree of accuracy.
One object of the present invention is to provide a novel method and apparatus for measuring the mass and/or weight of individual objects capable of being implemented at a high rate and with a high degree of accuracy in such measurements. Another object of the invention is to provide such a method and apparatus particularly useful for measuring the weight of small diamonds or other precious stones.
According to one aspect of the present invention, there is provided a method of measuring the mass of individual objects, comprising: conveying the objects towards an oscillatable probe having a predetermined mass and a vacuum port of smaller dimensions than those of the objects; applying vacuum to the vacuum port so as to attract and hold thereto one of the individual objects to thereby add its mass to the mass of the oscillatable probe; measuring the oscillating frequency of the oscillatable probe while the individual object attracted thereto is held by the vacuum applied to the vacuum port; utilizing the measured oscillating frequency of the probe and the object attract thereto to compute the mass of the object; and releasing the vacuum to release the object from the vacuum port preparatory for using the probe to measure the mass of another one of the individual objects.
According to further features in the preferred embodiments of the invention described below, the vacuum port has a mouth of conical configuration of larger dimensions than the objects.
According to further features in the described preferred embodiments, the probe includes a piezoelectric device. In one described preferred embodiment, the piezoelectric device generates an electrical output by the impact of the object when attracted to the vacuum port, which electrical output is at the oscillating frequency measured and utilized to compute the mass of the individual object. In another described embodiment, the piezoelectric device is driven at a first frequency which frequency is changed by the mass of the object when attracted to the vacuum port, the change in frequency being measured and utilized to compute the mass of the individual objects attracted to the vacuum port.
According to further features in the described preferred embodiments, the oscillating frequency of the probe is measured after a predetermined time delay following the contact of the object with the vacuum port.
According to further features in one described preferred embodiment, the probe overlies the objects such that the objects are moved against gravity towards the vacuum port by the vacuum at the vacuum port.
In another described embodiment, the probe underlies the objects such that the objects are moved with gravity(rather than against) gravity towards the vacuum port by the vacuum at the vacuum port.
According to another aspect of the present invention, there is provided apparatus for measuring the mass of individual objects within a predetermined range of sizes, comprising: an oscillatable probe having a predetermined mass and a vacuum port of smaller dimensions than those of the objects; a conveyor for conveying the individual objects towards the probe; a vacuum source for applying vacuum to the vacuum port of the probe so as to attract and hold thereto one of the individual objects to thereby add its mass to the mass of the probe; and an electrical measuring system for measuring the oscillating frequency of the probe while the object attracted to its vacuum port is held thereto by the vacuum at the vacuum port, and for utilizing the measured frequency of the probe and object to compute the mass of the object.
As will be described more particularly below, the method and apparatus constructed in accordance with the foregoing features are particularly useful for measuring the mass or weight of small diamonds or other precious stones, such as diamonds of less than 100 points (1 carat).
Further features and advantages of the invention will be apparent from the description below.